This invention relates generally to the art of tires and, more particularly, a method of designing a tire tread unit that, when incorporated in succession in a tread pattern, provides the tire with acoustically acceptable characteristics.
The tread of conventional vehicle tires typically comprises a plurality of load bearing tire tread units separated by a network of grooves. The tread block units are repeated in succession about the circumference of the tire to produce the tread pattern. As the tire rolls over a road surface, the tread units move into and out of engagement with the road surface causing disturbances in the surrounding air molecules that generate sounds. For any given tread pattern, a certain amount of acoustic energy, or xe2x80x9ctire noisexe2x80x9d is produced.
During the design phases of a tread pattern, the ability of the tire tread to produce an acceptably low noise level at tread passage frequency is an important consideration. To this end, much effort has been directed to the reduction of objectionable tire noise with emphasis on redistributing the energy produced by the tire tread at tread passage frequency over a broad band frequencies. In the past, this has been accomplished by a technique of applying pitches of different lengths in such a way that energy distribution over the frequencies is as spread-out as possible. This arrangement of pitches of variable lengths is called xe2x80x9cpitch sequence.xe2x80x9d In contrast, if tread units of constant pitch length are used, the sound generated is dominated by pure tones at tread passage frequency and its integer multiples.
Thus, in the past, the initial tread unit was designed to satisfy non-sound criteria such as, for example, wear-resistance, wet/dry traction and rolling resistance. During the creation of the tread pattern, a pitch sequence was then applied. Since pitch sequences were created independent of tread unit designs, the tread pattern produced then had to go through an iterative process of analytical evaluation and modification to obtain the best acoustic arrangement.
In a method of developing a tire tread pattern according to the present invention, the initial tread unit is designed to satisfy certain sound criteria. Specifically, if a tread unit design satisfies this criteria, it may be repeated in succession about the circumference of the tire to produce the tread pattern. The tread pattern produced mathematically eliminates the noise at tread passage frequency regardless of the pitch sequence used to produce the tread pattern. Analytical evaluation and modification of the tread pattern after its creation is not necessary.
More specifically, the present invention provides a method comprising the steps of importing a tread unit design geometry, simulating the impact of the tread unit design on a road surface, determining the number of pulses contained in the simulated impact, and analyzing, based on the number of pulses, whether the tread unit design satisfies a predetermined acoustic criteria. If a tread unit satisfies the acoustic criteria, it may be repeated in succession about the circumference of the tire to develop a tire tread pattern. Otherwise, the method may be repeated with a modified tread unit until the predetermined criteria is satisfied.
The step of simulating the impact of the tread unit design on the road surface may comprise the steps of digitizing the tread unit design, constructing a model using the digitized tread unit, and generating tread impact signals using the impact signa. The step of determining may comprise using Fast Fourier Transform (FFT) to determine the number of pulses contained in the simulated tread unit impact design. The predetermined criteria may comprise multiplying the number of pulse in the impact signal by the number of tread units in the tread pattern and determining whether this product is greater than a predetermined value, this value being, for example, 100.
The present invention provides these and other features hereinafter fully described and particularly pointed out in the claims. The following description and drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed.